Emergy evaluation of Mai Po mangrove marshes

Ecological Engineering 16 (2000) 271 – 280

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Emergy evaluation of Mai Po mangrove marshes P. Qin a, Y.S. Wong b,*, N.F.Y. Tam b b

a Department of Biology, Nanjing Uni6ersity, Nanjing 210093, PR China Department of Biology and Chemistry, City Uni6ersity of Hong Kong, Tat Chee A6enue, Kowloon, Hong Kong

Received 5 January 1999; received in revised form 25 February 2000; accepted 3 March 2000

Abstract This study is an emergy evaluation of Mai Po mangrove marshes. The important emergy indices of the system are as follows, the total output emergy of the marshes is 26.39 × 1017 sej/year; its macroeconomic value is 25.87 ×105 per year (in 1988 Hong Kong); its emergy density is 6.94 × 1011 sej/m2 per year; and its investment ratio (IR), environmental loading ratio (ELR), yield ratio (YR) are 0.48, 1.03, and 3.10, respectively. The emergy of education function in Mai Po was tentative calculated as 125.65× 1017 sej/year, its macroeconomic value is 123.19 × 105 $ per year (in 1988 Hong Kong), in which the knowledge distribution is outstanding, about 99.26 ×1017 sej/year, the macroeconomic value is 97.31 ×105 $/year (in 1988 Hong Kong), occupied 92% of all investments of whole education system. These data show that used emergy of per area in Mai Po is high and the management and education function of the natural reserve is good, but environmental loading is high. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Emergy evaluation; Mai Po; Natural reserve; Mangrove marshes

1. Introduction The Mai Po marshes are the largest remaining and most important wetland in Hong Kong. Its total area is 380 ha, including 250 ha ponds and 130 ha mangrove marshes. In September 1995, the Mai Po marshes and the inner Deep Bay were listed under the convention on Wetlands of International Importance especially as Waterfowl Habitat (the Ramsar Convention). A wide variety of habitat types with higher productivity of mangrove marshes, distinguished tidal shrimp ponds * Corresponding author. Tel.: + 852-2788-9377; fax: + 8522788-9377. E-mail address: [email protected] (Y.S. Wong).

(called gei wai by the locals) and a quiet and safe mudflat attracts a great deal of bird, Over 60 000 winter birds used the area in January 1996 (The Nature Conservation Bureau and Wetlands Advisory Service, 1997). This is a wonderful landscape in Mai Po. The marshes also draw much interest from a lot of people including scientists which make multi-discipline researches, for example, productivity and nutrients of mangrove marshes (Lee, 1989a,b, 1990a,b; Tam et al., 1990, 1998; Anderson, 1992), ecology of gei wai and fish ponds (Poovachiranon, 1986; Lee, 1989b; Aspinwall et al., 1996; Young and Chan, 1997), the birds and biodiversity in Mai Po marshes (Melville and Morton, 1983; Lee, 1986; Chalmers,

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1989, 1990, 1992), etc. The rough values of gei wai and fish pond, and the education significance of Mai Po have been evaluated and appraised (Axell, 1983; Nelson, 1993), but nobody is concerned to estimate the ecological – economic benefits (real wealth) in Mai Po with emergy analysis. Using the monetary cost of reinforcing nature as a measure of its value underestimate the wealth required for replacement (Jansson, 1984; Odum, 1996), because the major free environmental contributions are not included in the cost. A science-based evaluation system is now available to represent both the environmental values and the economic values with a common measure. This is emergy evaluation, which measures the energy of one type directly and indirectly used in the production to generate a product, whose units are solar emjoules (sej) Odum, 1988. This evaluation provides a quantitative way to find what policies and patterns for humanity and nature are sustainable, with less trial and error, because they tend to anticipate self-organization for maximum benefit and prosperity. In recent years, research using emergy evaluation has been active, including national and regional emergy analysis of environment, economy and public policy (Huang and Odum, 1991; Lan and Odum, 1994; Ulgiati et al., 1994; Brown and McClanahan, 1996); emergy evaluation of ecosystem and economic system (Odum, 1984; Gunderson, 1989; Bastianoni and Marchettini, 1996; Eum et al., 1996; Sohn et al., 1996; Tong, 1996; Day et

al., 1997) emergy theory research (Odum, 1983, 1996; Jorgenson et al., 1995; Patten, 1995; Tiezzi et al., 1996); etc. But there was less emergy evaluation on mangrove marshes (Gunderson, 1989), of course, not Mai Po mangrove marshes. In this study, emergy analysis is used to evaluate the integrative ecological–economic benefit of Mai Po marshes and the real wealth of its ecosystem, education function. The sustainability policy and manner of the marshes will be briefly suggested.

2. Methods

2.1. Study area The Mai Po marshes lies in 22°30%N, 114°00%E, on the edge of Deep Bay at northwestern part of Hong Kong, are located to the east of the Zhujiang River estuary (see Fig. 1). Its total area is 380 ha, including 250 ha ponds and 130 ha mangroves. In fact, Deep Bay is shallow, its average depth is only 3 m and the deepest depth is 6 m. Its largest tide difference is only 2.8 m, so there is a wide mudflat when the tide receded. The mangrove at Mai Po is the largest stand of mangrove in the territory and covers an area of 130 ha. The mangrove is located in transition of the inter-tidal mudflat and the gei wais. A total of six species of mangrove are found and these are Kandelia candel, Aegiceras corniculatum, A6icennia

Fig. 1. The position of Mai Po Natural Reserve in Hong Kong. A, Mai Po Natural Reserve; B, the district of Hong Kong; C, the continent of China.

P. Qin et al. / Ecological Engineering 16 (2000) 271–280

marina, Acanthus ilicifolius, Excoecaria agallocha, and Bruguiera gymnorrhiza. Among them the species of K. candel is the largest population in Mai Po. The productivity of mangrove ecosystem is relatively high and supports a high diversity of organisms. The most prominent one will be the colorful fiddler crab, Uca sp. and their burrows can be easily seen under the mangrove. Mangrove barnacle and snail are also abundant around the mangrove stem. A wide variety of habitat types can be found within the reserve that includes natural and manmade habitats. In the center of the reserve there are the man-made tidal shrimp ponds, called ‘gei wai’. They are large rectangular ponds (each area is about 10 ha) surrounded by dykes with one sluice gate for each pond on the seaward side to control the water inflow and outflow between the bay and the ponds at different tides. The central part of the gei wai is covered by vegetation dominated by the mangrove species and the reeds (Phragmites sp.). Fallen leaves as an organic input and shrimp larvae from the Deep Bay make the gei wai a self-sufficient system for shrimp production. Within the gei wai, the rapid accretion rate means that the channel around the edge of each pond has to be dredged every 10 – 12 years, so that a water column of approximately 1 – 1.5 m is maintained for prawn production. So Mai Po is a paradise of birds as feeding, roosting, breeding and nesting grounds as well as refueling station for migratory.

2.2. General methodology for emergy analysis The general methodology for emergy analysis is a ‘top-down’ systems approach (Odum, 1988, 1996).

2.3. Determining the important emergy indices In this study, a series of emergy indices will be determined. Among them the emergy investment ratio, environmental loading ratio and the net emergy yield ratio (YR) are rather important, because they reflect directly the relationship between economic and environmental subsystems, and ecological–economic benefit.

273

The emergy investment ratio (IR) is the ratio of feedback inputs (F) to all emergy derived from local sources (the sum of R and N), where R is local renewable emergy and N is the emergy from local nonrenewable sources. IR=

F (R +N)

The name is derived from the fact that it is a ratio of emergy ‘invested’ from the economy to resident emergy. The larger the investment ratio the greater the intensity of development. The environmental loading ratio (ELR) is the ratio of nonrenewable emergy (N+ F) to renewable emergy (R) as follows: ELR=

(N+ F) R

Low ELR reflects relatively small environmental loading, while high ELR suggests greater loading. The emergy YR is emergy of yield divided by the emergy of all the feedback from the economy (e.g. tourism income, several funds and services in this study), i.e. YR= (R+ N+ F)/F (in this system the output emergy is calculated by summing emergy inputs). The emergy YR of each system is a measure of its net contribution to the economy.

2.4. Determining the real wealth of education function in Mai Po The real wealth of education function in Mai Po is important to evaluate the synthetic effect of the system. The emergy evaluation includes not only financial and material investments, environmental resources, but also intellectual. In this study, the knowledge contribution is calculated tentatively as the intellectual investment. The major knowledge contribution in Mai Po is derived from its staffs, the emergy of knowledge contribution per individual is as follows, the total annual used emergy of Hong Kong divided by the population in different hierarchical level of education (Odum, 1996).

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Fig. 2. Emergy diagram for input and output of Mai Po. A, sun; B, wind; C, rain; D, tide and wave; E, mangroves; F, reeds; G, macroaiage; H, mud and sediments; I, ponds water; J, facilities and service; K, government budget; L, tourism income; M, aquaculture production; N, Nekton flow; O, waterfowl; P, education function; Q, market.

3. Results and discussion

3.1. Emergy e6aluation for input and output of Mai Po The aggregated system diagram in Fig. 2 illustrates the emergy inputs of renewable and nonrenewable sources, including sun, rain, tide, wave, mud sediments, ponds water, etc. The renewable sources are identified as rain (chemical) and wave, and the nonrenewable is as mud sediments. Wind, tide and sunlight are not added into the total renewable flow of emergy as same as ponds water is not added into the total nonrenewable flow (Table 1), since they are a part of the same coupled solar and earth based flows, it would be double counting to add the emergy of each. It is emphasized that both annual quantities of rainfall and wave in Mai Po are lower, its annual rainfall only 1400 mm, much less than the average level of Deep Bay (Chiu and So, 1986), and the extreme wave heights in whole Deep Bay is limited (Li and Lee, 1996). These are the geographical reasons, e.g. the rain shadow role of Mountain Tai Mo Shan and the shallow water depth of Deep Bay. Besides, the gross primary production (GPP) in Mai Po marshes includes mangrove, reed production, macroalgae and phytoplankton, but the quantity of last one is too little (the proportion in

GPP is only 0.9%; Lee, 1990b), and is not listed in the GPP items. K. candel materials are used to measure the mangrove productivity because it is the largest population in Mai Po. The emergy transformity of gross production estuary is used to the three primary production items in this study, i.e. 4700 sej/J (Odum, 1996). The investments include three items that are facilities and service supported by World Wildlife Fund (WWF), Hong Kong (HK) and several other funds, about US$ 4.1× 105 per year; government budget, about US$ 1.8× 105 per year; tourism income supported by the tickets of the natural reserve, about US$ 2.44× 105 per year. So the total investments are US$ 8.34×105 per year. The intellectual investment of the staffs in Mai Po is discussed in the education system of Mai Po. Aquaculture production which is shrimps and fishes harvested from and other fish ponds is an important outflow of the system and one of the major economic income of Mai Po reserve and about 400 kg/ha per year (Melville and Morton, 1983). The gei wai is self-sufficient system in which larvae of shrimp and fish come from the Deep Bay and their food from the litters of mangrove and reed, but its aquaculture harvest is not high and the contradictory between ecological and economic benefits emerged. According to the principle of priority in environment protection the commercial aquaculture production in Mai Po Natural Reserve could not be much developed. So WWF Hong Kong has purchased areas to restore the gei wais and maintain the ecological feature in the system. Now the total area of gei wai in Mai Po is about 150 ha. The Mai Po Natural Reserve is best known for bird watching in the cooler season. Over 70% of the birds recorded in the territory can be found at Mai Po. So evaluating the emergy transformity of waterfowls in Mai Po is very important. The wetlands are particularly important as feeding, roosting, breeding and nesting grounds as well as refueling station for migratory birds. Among these migrants are some globally threatened species such as black-faced Spoonbill (Plalatea minor), Saunders’ Gull (Larus saundersi ), Asiatic Dowitcher (Limnodromus semipalmatus) and spotted Greenshank (Tringa guttifer). The more com-

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Table 1 Emergy evaluation of principle flows for Mai Po Item

Raw data (J or US$)

Transformity (sej/U)

Solar emergy (×1017 sej) Macroeconomic value×105 1988 US$

Renewable sources (J) Rain, chemical a 2.63E+13 Wavesb 3.02E+13 Earth cyclec 3.80E+12 Total

15444 25889 29000

4.06 7.82 1.10 12.98

3.98 7.67 1.08 12.73

Nonrenewable sources (J) Mud and 1.40E+14 sedimentsd

3509

4.91

4.81

4.79E+13

4700

2.25

2.21

1.54E+13 0.06E+13

4700 4700

0.72 0.03 3.00

0.71 0.03 2.95

GPP (J) Mangrove productione Reed productionf Macroalgaeg Total In6estments ($) Facilities and serviceh Government budgeti Tourism incomej Total

4.10E+5

1.02E+12

4.18

4.10

1.80E+5

1.02E+5

1.84

1.80

2.44E+5

1.02E+12

2.48 8.50

2.44 8.34

1.3E+7

13.91

13.64

3.1E+7

9.36 23.27

9.18 22.82

Fishes, shrimps and crabs (J) Aquaculture 1.07E+11 productionk Nekton flowl 3.02E+10 Total

a Rain, chemical energy, area×rainfall×density×Gibbs number (Odum, 1996) =3.8×106 m2×1.40 m/year×1×103 kg/m3× 4.94×103 J/kg=2.63E+13 J/year. b Waves energy, 1/8×shore length×density×gravity×height2×velocity×3.154×107 (Odum, 1996) =0.125×3.5×103 m×1.03× 103 kg/m3×9.8 m/s2×(0.2 m)2×(9.8 m/s2×3 m)1/2×3.154×107 s/year= 3.02E+13 J/year. c Earth cycle energy, area×heat flow per area (Odum, 1996)=3.8×106 m2×1×106 J/m2 per year= 3.8E+12 J/year. d Mud and sediments energy, area×peaty sediments energy (Odum, 1996) = 3.8×106 m2×3.69×107 J/m2 per year= 1.4E+14 J/year. e Mangrove production energy, area×GPP of mangrove×standard energy value of C (Lee, 1990b; Odum, 1996) = 1.3×106 m2×1.1×103 gC/m2×8 kcal/g×4186 J/kcal=4.79 E+13 J/year. f Reed production energy, area×GPP of reed×standard energy value of C (Lee, 1990b; Odum, 1996) = 0.46×106 m2×1.0×103 gC/m2×8 kcal/g×4186 J/kcal=1.54 E+13 J/year. g Macroalgae energy, area×cover rate×GPP of algae×standard energy value of C (Lee, 1990b; Odum, 1996)= 2.5×106 m2×0.15×0.5×102 gC/m2×8 kcal/g×4186 J/kcal=0.06 E+13 J/year. h Management and services, the grants in facilities and management = 3.2×106 HK$ per year/7.75 (HK$/US$)=4.1 E+5 US$ per year. i Government budget, the grants in investments for production and leases =1.38×106 HK$ per year/7.75 (HK$/US$)=1.8 E+5 US$ per year. j Tourism income, the tourists number×ticket’s fee =26 962 per year×70 HK$/7.75 (HK$/US$)= 2.44 E+5 US$ per year. k Aquaculture production, area×aqua-production/m2 per year×dry rate×standard energy value (Homer, 1977; Melville and Morton, 1983) = 0.8×106 m2×4 0 g/m2 per year×0.2×4 kcal/g×4186 J/kcal=1.07 E+11 J/year. l Nekton flow in tidal channels, area×Nekton’s weight per m2/year×dry rate×standard energy value (Homer, 1977) =1.7×106 2 m ×5.3 g/m2 per year×0.2×4 kcal/g×4186 J/kcal= 3.02 E+10 J/year.

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Table 2 Calculation for emergy transformity of waterfowl in Mai Po Item

Raw data (J or Solar emergy US$) (×1017 sej/year)

Nektons Aquaculture production Investments Total Waterfowla The transformity of waterfowlb

3.02E+10 1.07E+11 8.34E+5($)

9.36 13.91 8.50

2.67E+10 1.03×108 sej/J

27.52

Support rate (%) Support’s emergy (×1017 sej/year) 100 100 50

9.36 13.91 4.25 27.52

a

Waterfowls (J), numbers×average weight×dry rate/replace time×standard energy value =20 000×0.8×103 g×0.2/2 year×4 kcal/g×4186 J/kcal= 2.67 E+10 J/year. b The transformity of waterfowl=27.52×1017/2.67×1010 =1.03×108 sej/J.

mon bird species are the herons and egrets, including the Chinese Pond Heron (Ardeola bacchus), little Egret (Egretta garzetta) and great Egret (Casmerodius albus). They can be found usually flying above the marshes or standing patiently in shallow water, waiting to catch the prey. During low tide, thousands of Sandpipers, Plovers, Curlew and Whimbrel can be seen feeding on the mudflats. By observation records Mai Po can support 20 000 waterfowls on ordinary occasions (the Nature Conservation Bureau, HK, 1997), the total energy of waterfowls could be obtained. Then considering the total emergy of supporting the birds (assuming the investments support rate is 50%) the emergy transformity of waterfowl in Mai Po was calculated as Table 2. There is a slight difference between the emergy of waterfowls and output flow in the system (Fig. 3), that is due to the evaluation of support’s emergy of investments on the waterfowls and the statistics of waterfowl number.

3.2. En6ironmental and economic contribution of Mai Po The emergy indices of Mai Po marshes are listed in Table 3. Among them renewable emergy flow (R), nonrenewable emergy flow (N) and flow of investment emergy (F) are 12.98 ×1017, 4.91 × 1017, and 8.50 ×1017 sej/year, respectively. The total emergy inflows of this system are 26.39×1017 sej/year, and it is also the system’s output (see Fig. 3). This is the principle of system’s emergy evaluation and output emergy is calculated by summing

emergy inputs to the same system. Using inputs for outputs assumes a priority that there are not unnecessary wastes and losses. The total emergy of environmental work is 17.89× 1017 sej/year. So the IR, ELR and the emergy YR of Mai Po are 0.48, 1.03, and 3.10, respectively. Comparing with Everglades National Park (Gunderson, 1989) whose IR, ELR and YR are 0.82, 0.82, and 2.22, respectively (Fig. 4), it shows that the intensity of development (IR) in Mai Po Natural Reserve is less, but its ELR is relatively higher, and its net contribution to the economy (YR) is more. Their emergy density (ED) are 3.82×1011 (in Everglades National Park (ENP), USA), and 6.94× 1011 sej/m2 per year (in Mai Po Natural Reserve (MPNS)) which reflects the emergy of local resource per unit area in Mai Po is higher and the investment level per unit area of the natural reserves is corresponding. Anyway, the ecological buffer of ENP is much larger, because its area is three times of whole Hong Kong. It is not easy to keep the low level of development intensity and environmental loading, and the high level of biodiversity and net contri-

Fig. 3. Summary of emergy flows for Mai Po ( × 1017 sej/year).

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Table 3 Emergy indices for Mai Po Number 1 2 3 4 5 6 7 8 9 10

Description

Expression

Quantity

Renewable emergy flow Nonrenewable emergy flow Flow of investment emergy Total emergy inflows Total emergy of environmental work The investment ratio The environmental loading ratio The emergy yield ratio Emergy density HK emergy/$

R N F I= R+N+F E= R+N IR = F/E ELR=(F+N)/R YR= (R+N+F)/F Used emergy/area Used emergy/GDP (1988)

12.981017 4.911017 8.501017 26.391017 17.891017 0.48 1.03 3.10 6.941011 1.021012

bution to economy in a long term in Mai Po that is in Hong Kong with high economic level. So enacting a series of the local laws and policies to limit the land development of Mai Po and around it, and to reduce its environmental loading is very important and urgent for Mai Po.

3.3. E6aluating emergy for education function in Mai Po The great educational value of Mai Po is famous and this was one of the prime objectives with which WWF HK took over its management (indicated by the title — the Mai Po marshes Wildlife Education Center and Natural Reserve). Its education function is integrative, not only in teaching for students and children, in training for the management members of other reserves, but also in scientific tourism and bird watching. So all staff of the Reserve have served to integrate education, and the emergy of their knowledge contribution is a major fraction of education function in Mai Po. The emergy flows of education function and its accounting are illustrated in Fig. 5 and in Table 4, respectively. There are only 17 staff (three persons have Ph.D. or M.S. degree, three have B.S. degree and others are studying in their jobs) in the Reserve with 380 ha, but their knowledge contribution is rather high, about 99.26× 1017 sej/year and occupies 92% of all investments (107.76×1017 sej/year) and 80% of total input flows (or output flow) (125.65×1017 sej/year) in the whole education system. It is

sej/year sej/year sej/year sej/year sej/year

sej/m2 sej per US$

obvious that the output emergy of the education system is much more than that of the natural system in Mai Po, because the knowledge contribution per person per year is relative to his or her concentration of knowledge in past years. People including students and tourists could much benefit from the education function of Mai Po. It is interesting that tourists as same as the birds watched in annual census (usually in January) were more and more from 1988 to 1996. It shows that Mai Po’s habitat benefits waterfowls and the natural reserve also benefits tourists and students as its special landscape and scientific value. As the emergy density in Mai Po is higher (6.94× 1011 sej/m2) and its investment ratio is lower (only 0.48), so its potential for drawing more birds would be much.

Fig. 4. Comparison of emergy indices between MPNS and ENP USA. IR, investment ratio; ELR, environmental loading ratio; YR, emergy yield ratio; and ED, emergy density (E11 sej/m2 per year).

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278

Fig. 5. Emergy flows for education function in Mai Po (E17 sej/year). A, renewable sources; B, environmental work; C, nonrenewable storage; D, facilities and services; E, knowledge contribution; F, budget and tourism.

Mai Po Natural Reserve can rationally arrange the tourism, scientific investigation and study, and training with its high emergy resources to obtain much more education benefits.

4. Summary This study on emergy evaluation of Mai Po mangrove marshes has obtained a series of conclusions. First, the total output emergy of the marshes is 25.29 × 1017 sej/year, its macroeconomic value is 24.8×105 $ per year (in 1988 Hong Kong) and its emergy density is 6.94× 1011 sej/m2 per year, its IR, ELR, YR are 0.48, 1.03,

and 3.10, respectively. Second, the emergy of education function in Mai Po is 125.65× 1017 sej/ year, its macroeconomic value is 123.19× 105 $ per year (in 1988 Hong Kong), in which the knowledge distribution is outstanding, about 99.26×1017 sej/year, the macroeconomic value is 97.31× 105 $ per year (in 1988 Hong Kong), occupied 92% of all investments of whole education system. Third, these data show that used emergy of per area in Mai Po is higher, and the management and education function of the natural reserve is good, but environmental loading is high. Mai Po Natural Reserve can rationally arrange the tourism, scientific investigation and study, and training with its high emergy resources to obtain much more education benefits. Mai Po’s area is only one of the 40 marshes of Hong Kong but its importance far transcends their size. At one time such marsh extended along much of the shore of Hong Kong. Today the Mai Po is the largest surviving remnant. But now trading, industrial, and other development purposes in Hong Kong need new land development, especially in the low land. Mai Po has faced much stress. A large new residential area has been constructed adjacent to the marshes. An array of roads, sewer lines and other infrastructure has been built to serve these new urban areas. So enacting a series of the local laws and policies to limit the development of Mai Po and around it, and to reduce its environmental loading is very important and urgent for Mai Po.

Table 4 Emergy evaluating of education function service in Mai Po Note 1 2 3 4 5

Item

Emergy flows (×1017 sej/year)

E5$ (1988, ×105)

Environmental work Facilities and services Budget and tourism Knowledge contributiona Total (education function)

17.89 4.18 4.32 99.26 125.65

17.54 4.10 4.24 97.31 123.19

a In Hong Kong the population of Master and Ph.D. is about 20 823 people, the population of bachelor and corresponding degree is about 354 566 people and the population of studying on the job is about 428 316 people (resource from Lee, Yuan Hao, Education and Manpower Bureau, Government Secretariat, Hong Kong). The total used emergy of Hong Kong (1988) was 556.94×1020 sej/year (Lan and Odum, 1994). So average emergy per individual of the three populations are calculated, respectively, as follows: 556.94×1020 sej/year per 20 823= 26.75×1017 sej per individual per year (Master and Ph.D.); 556.94×1020 sej/year per 354 556= 1.57×1017 sej per individual per year (Bachelor); 556.94×1020 sej/year per 428 316 =1.30×1017 sej per individual per year (no degree). The total emergy of knowledge contribution of all staffs in Mai Po is, 26.75×1017×3+1.57×1017×3+1.30×1017×11= 99.26 sej/year.

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